The invention relates to a process for identifying deactivated surface areas of a basically flat electrode for electrochemical processes, especially an anode for electro-galvanizing plants for steel bands, and a device for the working of this process.
Titanium anodes coated with metal oxides of the platinum group are also used for electrogalvanizing steel bands which serve, for example, for the manufacture of galvanized automobile bodies. After a certain time the titanium anodes lose their activity and must be reactivated after removing. For this purpose the entire galvanizing plant must be shut down which temporarily paralyzes the entire production process. Hence, it is desirable to be able to assess during an intended standstill of the plant--which is in any way necessary due to different reasons--whether the anodes will last until the next intended standstill or whether they have to be immediately replaced for reasons of safety.
Presently, the following methods are used to assess if the anodes are still active or not:
(a) Measuring the thickness of the activated layer by means of X-ray fluorescent analysis (only possible during a standstill): This process is very time consuming and can hardly be applied for all anodes during a standstill. Despite a high remaining layer thickness the anodes can be inactive due to passivity below the active layer. Measuring is only possible where the diameter does not exceed 5 cm. Many individual measurings must hence be carried out and evaluated in order to assess an entire area of 1 m.sub.2, for example. PA1 (b) Measuring the potential (only possible during standstill): This process, too, is very time consuming and does therefore not permit measuring all anodes during standstill. Again, only a point-by-point measuring is possible. PA1 (c) Shutting down individual anodes during operation: This process permits a continuous measuring of the thickness of the layer of the coated zinc. If the layer is uneven, individual anodes are shut down. If this makes the coating more even these anodes are no more considered to be fit for operation. This process cannot be applied in every plant. The layers can also be uneven for reasons other then deactivated anodes. PA1 (d) Galvanizing during standstill of the band: If the steel band which during regular operation travels through the plant at a speed of 1 m/sec is stopped, the zinc distribution on the band corresponds to the anode activity. In the practice, the power is shutdown for reasons of safety immediately after the band is stopped. In order to carry out the process all safety measures must be suspended. The process is very expensive and can be applied only exceptionally.
Hence, the present state-of-the-art does not offer any reasonable possibility to rapidly determine if a certain anode (or a segment thereof) requires reactivation or can continue to be in operation until the next intended standstill.